间接空冷自然通风冷却塔抽力计算公式

Investigation on Draft Equation for Natural Draft Dry Cooling Tower

在电厂冷却塔的设计中,根据塔内外空气密度差计算塔内抽力应用较广泛,但缺少理论依据,且计算结果存在较大误差,Kroger算法考虑了相关作用因素的影响,计算精度较高,但计算形式复杂。以间接空冷自然通风冷却塔为模型,通过实验和数值模拟对比了塔内抽力密度差模型和Kroger模型的准确性,指出了后者计算抽力结果更准确的原因,其影响因素主要包括:冷却塔高度、环境大气温度及循环水进口温度。分析结果表明:当环境大气温度和循环水进口温度条件不变时,随冷却塔高度的增加,密度差模型较Kroger模型的相对误差随之增大,则计算的换热量误差亦增大。同理,在其他2个条件不变时,随环境大气温度的升高或随着循环水进口温度的降低,相对误差增大。分析结果为自然通风冷却塔抽力计算公式的适用范围以及不同条件下计算方法的选择提供了理论依据。

In the design of cooling tower,it is widely used to calculate the draft according to the difference of air density inside and outside the tower,but there is a lack of theoretical basis.The calculation results have errors in some cases.The Kroger model is more accurate but more complex.Taking the natural draft dry cooling tower as the analytical model,the accuracy of the density difference algorithm and the Kroger algorithm through the experiment and numerical simulation were compared in this paper.The results shows that the latter is more accurate in calculating the draft.The Kroger algorithm provides a mathematical theoretical foundation.What’s more,the factors why the error of density difference algorithm is slightly bigger than Kroger algorithm are analized that the height of cooling tower,the ambient air temperature and the inlet temperature of circulating water.The conclusions are that when the ambient temperature and the inlet temperature of the circulating water are constant,the relative error of the draft by the density difference algorithm increases with the height of cooling tower increasing compared to the Kroger algorithm,then the relative error of heat transfer rate increases.Similarly,when the other two conditions are constant,the relative error of draft increases as the ambient temperature increases or the inlet temperature of the circulating water decreases.This study lays a theoretical foundation for the design and calculation of the natural draft cooling tower.